In general, in order to block radiation, a metallic lead, iron, or concrete is used for the walls of facilities handling radiation, such as those of medical institutions. In this case, it is necessary to provide a room with a window when an equipment control room, an examination room, or the like is partitioned with concrete or the like. In addition, when an examination is performed by injection or inhalation of radiation-generating drug or the like into a subject, a protection screen is required for preventing the whole body of a doctor, a laboratory technician, a nurse, or the like from directly receiving radiation when observing the medical conditions of a subject close at hand, for example, by confirming the complexion and the pulse of the subject.
For ensuring the safety of the human body by blocking radiation, the window and the protection screen require abilities of blocking radiation from a radiation source, so-called radiation-shielding ability. Besides, if the existence of the subject cannot be precisely confirmed with eyes, various kinds of adverse effects will be caused. In the medical field, in particular, the examination results of the subject can be adversely affected. Thus, the window and the protection screen should be provided with visibility.
On the other hand, in recent years in the medical field, the execution of positron emission tomography (PET) examination, which can perform an early detection of cancer cells, has been promoted. Specifically, according to the following Non-patent Document 1, the PET examination represents the so-called “positron tomography”. It describes that the PET-CT device or the like is a new examination method to diagnose the cause of illness and the symptom by taking the activity of the heart, brain, or the like as a tomogram.
As a diagnostic drug used for the PET examination, there is a compound in which a sugar component is labeled with a positron nuclide and the compound depending on the purpose of the examination is prepared in the form of an “injection” or an “inhalant”. Thus, the compound can be incorporated into the body by intravenous injection or breathing, so a tomogram can be taken by the PET-CT device. In this case, positrons are released from the labeled compound and then collide with an electron to generate radiation. In other words, 18F-FDG, for example, causes a gamma ray which is equivalent to energy of 0.511 MeV, so the detection of the gamma ray by the PET-CT device enables to specify the presence or absence of cancer cells, a focus size, and the like.
Therefore, under the environment of the medical examination involving the PET examination, the subject given a diagnostic drug generates gamma rays in every direction, so an essential requirement is to prevent the body of an examiner such as a doctor from directly being exposed to the gamma rays.
Further, representative examples of the radiation-shielding windows and radiation-shielding protection screens conventionally known in the art include a PbO-containing glass with high radiation-shielding property disclosed in Patent Document 1 described below.
[Patent Document 1] JP 02-212331 A
[Non-patent Document 1] General study business for medical technology assessment of Grant-in-Aid for Scientific Research funded from the Ministry of Health, Labor and Welfare, 2005, Study group for the security of the radiation safety in the PET examination institution, Ed., Guide line for the security in FDG-PET examination (2005) URL: http://www.jsnm.org/report/pet-anzen-gl.pdf